Question: Simplify the following expression: $z = \dfrac{10y}{9} + \dfrac{y}{8}$
Solution: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9$ and $8$ $\lcm(9, 8) = 72$ $ z = \dfrac{8}{8} \cdot \dfrac{10y}{9} + \dfrac{9}{9} \cdot \dfrac{y}{8} $ $z = \dfrac{80y}{72} + \dfrac{9y}{72}$ $z = \dfrac{80y +9y}{72}$ $z = \dfrac{89y}{72}$